This paper presents, direct liquid-cooled power module with circular pin-fin, a inverter parallel cooling system for high output EV/FCEV. The direct cooling system of the conventional inverter is designed to supply the coolant along the direction in which the heating element such as Si-chip is disposed and discharge the coolant to the opposite side. In the case of an inverter, the higher the output, the coolant temperature difference between inlet and outlet becomes larger due to the heat exchange of the heat generating element, so that a temperature deviation occurs depending on the position of Si-chip. Since the durability is judged on the basis of Si-chip having the highest temperature, the inverter itself must be replaced or discarded due to the durability of the inverter even though Si-chip which has a good cooling can be driven further. A simple way to solve this problem is to increase the cooling flow rate, but this leads to an excessive increase in pressure loss due to circular pin-fin. The parallel cooling system concept is a feasibility study with the goal to improve power module chip’s junction temperature and pressure loss in cooling channel at once at the same flow rate. A number of geometries of parallel cooling channel have been modeled in order to optimize. The best geometry achieved decrease of 1.1% in chip’s temperature and 35.6% in pressure loss at 8LPM coolant flow rate on 450V, 8kHz switching frequency.